Many researchers have investigated the possibility of providing wide-band communication to each home or household. Such wide-band communications include: high speed transactional data and internet access, "media on demand" or selective real-time continuous, streamed communication, such as audio, video or both (e.g., video on demand), real-time, two-way streamed communication, i.e., voice, audio and/or video (e.g., telephone, video phone, etc.) or some combination of these communications. Currently in the United States, Japan, Europe and other developed countries of the world, most homes are connected by a traditional telephone line to a telephone network. Many of these homes also have a Community Antenna Television (CATV) or "cable TV" connection. Most telephone lines installed at customer premises only support "plain old telephone service." These telephone lines are designed to have a limited bandwidth of about 3 kHz. On the other hand, most cable network links to subscriber locations are coaxial lines. The limitation on bandwidth to such subscriber locations is mostly dictated by the bandwidth of the coaxial and optical trunk lines that connect the subscriber locations to the cable head end or source transmitter of information. The bandwidth of existing trunk lines ranges from 350 MHZ to 1 GHz and is usually approximated as 750 MHZ for an average cable network. Consider that a video signal alone compressed to an average acceptable fidelity, according to the MPEG standard, requires at least a 1.5 Mbit/sec bit rate. The widely deployed plain old telephone service lines can currently support only about a 33.4 Kbit/sec bit rate. As such, the currently deployed cable network infrastructure is more capable of supporting high bandwidth communication to the subscriber locations than the currently deployed telephone network.
FIG. 1 shows a cable network 10. Signals received at satellite receiver 12 or via trunk line 14 are fed to head end 16. The head end 16 may process the signals. Most importantly, the head end 16 selects amongst the received video program signals, modulates each of the signals onto a different carrier signal having a different carrier frequency, and transmits the carrier signals onto the shared medium 18. The shared medium 18 is composed of individual links 20, which may be optical fibers or coaxial cables. An output trunk line link 20 from the head end 16 is connected to an amplifier/splitter A1. Three links 20 (preferably trunk line links) are outputted from the amplifier A1, to the amplifiers A2, A3 and A4, respectively. Each of these links are downstream links relative to the amplifier A1 whereas the link to the cable head end 16 is an upstream link. Additional links 20 are provided for connecting the amplifiers A5, A6, A7, A8 and A9. Links 20 of the shared medium 18 (preferably thinner gauge coaxial cable as may be used in trunk line links) are also provided for connecting terminal equipments, such as set top boxes or cable modems, TE1, TE8 and TE15 to the amplifier A2, for connecting terminal equipments TE2, TE6 and TE7 to the amplifier A4, for connecting terminal equipments TE9, TE16 and TE17 to the amplifier A5, for connecting terminal equipments TE3, TE4 and TE5 to the amplifier A6, for connecting terminal equipments TE12, TE13 and TE14 to the amplifier A7, for connecting terminal equipments TE10 and TE11 to the amplifier A8 and for connecting terminal equipments TE18, TE19 and TE20 to the amplifier A9. The overall topology of the cable network 10 is a tree configuration with the head end 16 at the root of the tree and the terminal equipments TE1-TE20 at leaves of the tree.
Cable networks are currently used primarily to deliver communicated information in a single direction, namely, from the head end to the terminal equipments at the subscriber locations. Typically, the information is traditional broadcast video programming, wherein each video program or "television channel" is modulated onto a separate carrier frequency in the band from 50-750 MHZ with a 6 MHZ bandwidth. The band from 0 to 50 MHZ (actually, the sub-band of 5-40 MHZ) is often used as a back channel for communicating short control messages from the terminal equipments to the head end, such as requests to receive pay per view events. The head end can also transmit authorization control messages to the terminal equipments in this band for enabling them to descramble or decrypt a pay per view event.
In the course of several standards bodies proceedings (e.g., Digital Audio Visual Council, or DAVIC, IEEE 802.14, etc.), a number of architectures have been proposed for providing subscriber location wide-band communication using a cable network. According to the DAVIC proposal, the 50-450 MHZ band is allocated for analog broadcast video programming, the 450-750 MHZ (or higher) band is allocated for digital broadcast video programming and the 5-45 MHZ band is allocated for wide-band terminal equipment communication. Either Quadrature Phase Shift Keying (QPSK) or Quadrature Amplitude Modulation (QAM) may be used for modulating wide-band terminal equipment communicated information onto 6 MHZ bandwidth carrier frequencies. See DIGITAL AUDIO VISUAL COUNCIL, DAVIC 1.0 SPECIFICATION, PART 8: LOWER LAYER PROTOCOLS AND PHYSICAL INTERFACES, rev. 3.1 (1995). The proposed multiple communication multiplexing techniques can be categorized as time division multiplexing (TDM) or frequency division multiplexing (FDM). Furthermore, the proposed techniques for allocating communication channels and resolving contention (when more communications than available channels contend to use the channels) can be categorized as polling or random access techniques. Each of these techniques is briefly described below.